The present invention relates to a method for determining the wheel geometry and/or axle geometry of motor vehicles using an optical measuring device, with which—while optionally taking into account reference features and vehicle body features—an image recording system that includes at least two image recording devices for creating digital images is used to assign at least two recording points to each other and perform referencing relative to the measurement space, an object section including the wheel to be measured is registered from different perspectives, and the position of wheel features in the three-dimensional measurement space is evaluated in the measurement.
A method of this type is described in DE 197 57 763 A1 and EP 1 042 643 B1. Using these known methods, the axis of motion, and data on the wheel geometry and axle geometry are ascertained with the aid of image recording devices—cameras, in particular—a reference feature system at the test station, and optical features on the motor vehicle and the vehicle body. According to DE 197 57 763 A1, the measurement is carried out with the vehicle at a standstill. According to EP 1 042 643 B1, however, the motor vehicle is driven past the measurement device with the image recording system. Based on a detection of the motor vehicle and the reference feature system, the measuring device references the system in the measurement space relative to the measurement station. Features that have been applied intentionally in the reference feature system (for referencing the measurement device), features on the wheel or wheels to be measured and on the vehicle body, and existing features are utilized to carry out the methods. Additional effort is required to adapt special features on the wheel and the vehicle body and in the reference feature system, but doing so is advantageous because it allows the features to be ascertained unambiguously, thereby resulting in a high level of measurement accuracy. The method is enhanced, however, by the fact that this known measurement device allow features to be applied to the vehicle body and the wheel, in particular, that do not need to be adjusted, and that are lightweight.
The highly accurate determination of the wheel geometry and axle geometry of motor vehicles is becoming increasingly significant as suspension technology continues to improve. New and more finely tuned methods for adjusting toe and camber of individual wheels require that the measurement device be highly accurate. Measurement devices that require laborious installation and adjustment of the measurement device on the wheel for use with the methods described above are widespread.
Further methods have been developed based on the publications listed above, as described, e.g., in DE 199 34 864 A1 and DE 100 50 653 A1. While the former publication presents, e.g., a special method for determining the axis of motion of the motor vehicle based on a trajectory of at least one vehicle body feature, more detailed explanations of various procedures are described in DE 100 50 653 A1 for referencing the measurement device with the measurement station, and assigning the recording locations to each other (via position and direction, also referred to as orientation).
Publication EP 0 895 056 A2 describes the use of structures present on the motor vehicle anyway, particularly the edge of the rim, for measuring the axis. To determine the 3D position and the position of the wheel plane, the position of the plane of the rim edge is derived from the two images taken by two cameras by identifying the rim edge in a single image of a pair of images based on a processing of maximum gray-value transitions of several significant features of the rim edge and, based on this, calculating the ellipse using five points on the rim edge that was depicted. A procedure of this type, which is known per se from image processing, with which edges are ascertained based on abrupt gray-value transitions, makes it difficult to obtain an accurate measurement of the geometric data. It also creates problems associated with avoiding disturbing influences caused by changing illumination situations.
The object of the present invention is to provide a method of the type described in the preamble, with which exact measurement results of the wheel geometry and/or axle geometry are obtained with a minimum of adjusting effort and without the need to make additional adaptations for measurement marks.